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Hi, I have replaced the balance staff on a Seiko 5606. Old staff had lots of end shake and both pivots were ground flat. The new Ronda staff is much better with just the right end shake but I see differing amplitude (20 Deg difference) and rate dial up/ down (11 SPD difference). I investigated the pivots and found one of them that is pretty much flat while the other is slightly rounded. Is this to be expected on a new staff? I would have thought they would be shaped and polished out of the packet. All help appreciated, Steve.

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This is not unusual especially with vintage movements. Generally, the watch repairer will want to draw the amplitude to be as close as possible to the side positions (PF, PU etc) and vice versa. So if amplitude is too great then it can be reduced by flattening the pivots and if it's low then it may benefit from being rounded off more.

Of course, this is not the only factor governing amplitude and rate but it is one to take into consideration as many vintage watches were timed by hand by a technician when first manufactured resulting in no two watch movements being identical - try swapping the balance assembly between two identical Smiths movements for example - I would be surprised if there wasn't a noticeable difference.

Therefore - more work can be involved when fitting balance staffs to vintage watch movements and timing it to a reasonable standard - sometimes lots of pushing, pulling and tweaking until you get a good result.

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6 minutes ago, Mark said:

This is not unusual especially with vintage movements. Generally, the watch repairer will want to draw the amplitude to be as close as possible to the side positions (PF, PU etc) and vice versa. So if amplitude is too great then it can be reduced by flattening the pivots and if it's low then it may benefit from being rounded off more.

Of course, this is not the only factor governing amplitude and rate but it is one to take into consideration as many vintage watches were timed by hand by a technician when first manufactured resulting in no two watch movements being identical - try swapping the balance assembly between two identical Smiths movements for example - I would be surprised if there wasn't a noticeable difference.

Therefore - more work can be involved when fitting balance staffs to vintage watch movements and timing it to a reasonable standard - sometimes lots of pushing, pulling and tweaking until you get a good result.

Thanks Mark, I appreciate your input. I have ordered a Bergeon pivot rounding tool as I do not have any Jacot or lathe (or the skill to use either). I will report back with pictures of the rounded pivot and hopefully some amplitude gain. Steve.

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